Pagers are compact radio receivers, typically incorporating a display, that may be carried on a person, to receive and display short radio messages directed to that pager. The messages are normally originated by a person who calls a particular telephone number of a paging service and is connected, directly or indirectly, to a radio transmitter which broadcasts the desired message coded to be received only by the intended pager.
Pagers may be divided into numeric pagers and alpha-numeric pagers. For a numeric pager, a caller dials a unique telephone number assigned to that pager. When that call is connected, the user is instructed to enter the digits of a telephone number that the owner of the pager should call. These numbers are entered using the keypad of the telephone and are encoded in dual tone modulated frequency encoding ("DTMF") used by most tone dialing telephones. A message incorporating the telephone number entered by the caller is automatically transmitted to the pager associated with the number dialed by the caller.
One advantage of a numeric paging system is that the caller may use a conventional telephone.
For an alpha-numeric pager, the caller dials a number common to many pagers. To identify the particular pager to which a message is to be sent, the caller then enters a pager identification number ("PIN") unique to that pager. A short alpha-numeric message (numbers and/or letters) may be entered and transmitted to the indicated pager.
While the ability of the alpha-numeric pager to receive messages composed of both letters and numbers is an advantage over the numeric pager, this feature requires the caller to have access to a specialized alphanumeric entry device ("AED"). In contrast to a standard telephone, an AED incorporates a full typewriter-type keyboard of all letters and numbers. Further, the AED incorporates a text-type modem which encodes letters and numbers for transmission over the telephone lines according to an ASCII protocol and with a modulation system different from the DTMF system employed by a standard telephone to encode digits used for dialing.
The need for a specialized AED to initiate calls to an alpha-numeric pager substantially limits the flexibility of the alpha-numeric pager.